Helium refrigerator and method for decontaminating the refrigerator

ABSTRACT

For use in a multi-stage refrigeration system an improved heat exchanger of a type having an hermetically sealed housing and including therewithin a pair of chambers defining a pair of concentrically related countercurrent passages extending therethrough. A particular feature of the invention is embodied in a decontaminating system which includes a circuit pneumatically coupled with a given heat exchanger and adapted to vent the heat exchanger to atmosphere and to flush the vented heat exchanger with a gas delivered under pressure and at ambient temperature so that frozen contaminants operatively are melted and simultaneously expelled from the system.

United States Patent Low et al. {451 Apr. 18, 1972 [54] HELIUM REFRIGERATOR AND 2,450,707 10/1948 Zwickl ..62/85 METHOD FOR DECONTAMINATING 3,360,955 1/1968 Witter ..62/6 THE REFRIGERATOR 3,421,331 l/ 1969 Webb ..62/6

[72] Inventors: George M. Low, Acting Administrator of Primary Examiner-William J. Wye

the National Aeronautics & Space Ad ministration with respect to an invention of lir yi n R. Wiebe, l4202 Qsborne Street. Panorama City, Calif. 91402 Filed: Feb. 5, 1971 Appl. No.: 112,999

US. Cl ..62/85, 62/80, 62/475,

62/6 Int. Cl ..FZSb 47/00 Field of Search ..62/85, 195,475,474, 6,80

References Cited UNITED STATES PATENTS Zwickl ..62/85 FROM C OMPPE S S 0 Attorney-John R. Manning, Monte F. Mott and Wilfred Grifka ABSTRACT For use in a multi-stage refrigeration system an improved heat exchanger of a type having an hermetically sealed housing and including therewithin a pair of chambers defining a pair of concentrically related countercurrent passages extending therethrough. A particular feature of the invention is embodied in a decontaminating system which includes a circuit pneumatically coupled with a given. heat exchanger and adapted to vent the heat exchanger to atmosphere and to flush the vented heat exchanger with a gas delivered under pressure and at ambient temperature so that frozen contaminants operatively are melted and simultaneously expelled from the system.

3 Claims, 2 Drawing Figures (we/1 PRESSURE 510E) %E r0 COMPRESSOR 5 CROSS/154D (Low PRESSURE 5105) ppm/,5 CAM 50 54 ATMOJH-IE/PE 46 [ST 8 l0 EXHAUST VALVE sxczj li c s g 3; /6 MET VALVE PR 18 I972 FROM COMPRESSOR (ma/1 PRESSURE 5/05) moss/1540 W1 zzz'zzzfizfi 50 5 ATMOSPHERE 7 4 y/ EXCHANGE? g 45 45 510w pow/v c0/v0u/r Hi2? EXCHANGE? R0 3 RD l5 EXCfZf/ifZE/P +-l R6 0 42 0 46 w i 265 QOQL 44 R W TO COMP/953505 (IN TERMED/A TE PRESSURE) WILVE DR VE CAM EXHAUST VALVE INLE 7' VAL E ERV/N R. Wi

ORIGIN OF INVENTION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 USC 2457).

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention generally relates to multi-stage cryogenic refrigeration systems and more particularly to an improved heat exchanger for use in achieving a rapid decontamination of such systems.

2. Descriptionof the Prior Art Refrigeration systems of the type with which the heat exchanger of the instant invention is employed generally are well known. For example, US. Pat. No. 3,421,331 discloses a system wherein liquid helium temperatures are achieved by utilizing a plurality of series-connected heat exchangers, each having an hermetically sealed housing including therewithin a pair of concentric chambers defining a pair of counter-current passages extending therethrough for conducting in a simultaneous fashion oppositely flowing streams of gas. Each of the heat exchangers is, in turn, associated with a refrigeration stage of a multi-stage heat engine, with ultimate cooling being achieved in a Joule-Thompson valve.

In such units gas from a compressor is delivered through a series of heat exchangers, cooled in successive stages, and ultimately delivered through a filter to a Joule-Thompson valve wherein maximum cooling is achieved. The net effect is that the temperatures of the gas are lowered to a temperature approximating that of liquid helium and employed in cooling MASERS and the like.

In practice, helium gas at high pressures and substantially ambient or room temperature is delivered to the system in an input flow, cooled to around 70 K as it is discharged from a first heat exchanger, further cooled to approximately 15 K, as it is discharged from the second heat exchanger, and ultimately cooled to approximately 43 K at the Joule-Thompson valve. The flow of gas from the Joule-Thompson valve is returned in a counter flow through the plurality of heat exchangers for achieving a pre-cooling of the gas being delivered in an input flow. Since the heat exchangers are fully described, in terms of their function and configuration, in the aforementioned US Pat. No. 3,421,331, a detailed description is here omitted.

With the advent of refrigeration systems of the type described in the aforementioned Us. Letters Patent, the downtime required for system repair has been greatly reduced and in many instances substantially eliminated. However, there is a tendency for such systems to acquire water vapor, oil vapor and various types of gaseous contaminants. These vapors then condense and subsequently freeze within the heat exchanger causing the systems to be rendered substantially inoperative. As a consequence, it is still necessary to terminate the operation of the systems for purposes of clearing the systems of the contaminants in order to insure a continued effective operation of the system. This then requires a warming period sufficient to permit the system to warm to ambient room temperatures in order to convert frozen contaminants to a fluid which can be flushed from the system for achieving a decontamination thereof. Since refrigerators of the type hereinbefore discussed frequently are employed in deep-space communications networks, it is imperative that down-time encountered be substantially reduced, and preferably eliminated.

Heretofore, in order to effect a decontamination of systems of the aforementioned type, several hours were required in warming the system to a temperature sufficient to achieve decontamination. Once decontamination was achieved, the

period required in again cooling the system to 4.4 K involved even a greater amount of time. Hence, there currently exists a need for an improved practical refrigeration system capable of achieving decontamination within a minimal time period.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of the instant invention to provide in a refrigeration system of the type including therewithin a plurality of series-connected heat exchangers, an improved heat exchanger which overcomes the aforementioned difficulties and disadvantages.

It is another object of the instant: invention to provide in a counter flow refrigeration system of the type including a plurality of series-connected heat exchangers a practical blowdown circuit including a heat exchanger which effects a rapid warming of an associated heat exchanger without substantially altering the temperature of the remaining series-connected heat exchangers.

It is another object to provide within a counterflow refrigeration system of the type adapted to function at cryogenic temperatures, an improved heat exchanger including an associated blow-down circuit.

Another object is to provide a practical method of decontaminating counter flow refrigeration systems of the type including a plurality of series-connected heat exchangers and adapted to function at cryogenic temperatures.

These and other objects and advantages are achieved through the use of an improved heat exchanger including an associated valved blow-down circuit for delivering thereto gas at elevated pressures and ambient temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of the refrigeration system with which a heat exchanger of the: instant invention is employed for accommodating rapid decontamination.

FIG. 2 is a partially sectioned view of the first heat exchanger illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a refrigeration system having coupled therewithin an improved heat exchanger 10 for use in achieving a rapid decontamination of the system.

The structural details of the system depicted in FIG. 1 are more fully disclosed in the aforementioned US. Pat. No. 3,421,331 and therefore are not here repeated. However, in order to more fiilly appreciate the instant invention, it is be lieved that a brief discussion of the operation of the system shown in FIG. 1 will be beneficial.

As illustrated, helium gas, under pressure, is delivered to the system from the high-pressure side of a given compressor, not shown. The gas is delivered through a plurality of series-connected heat exchangers 10, 12 and 14-, designated first, second and third heat exchangers, respectively, by a delivery conduit, generally designated 15. Simultaneously, the gas is delivered to a heat engine or gas-balancing refrigerator 16, which includes a first refrigeration stage 18 mechanically connected to a second coaxially related refrigeration stage 20. A filter 22 is provided within the conduit 15 for removing contaminants, not previously removed, prior to the gas being delivered to a final cooling stage 23 which includes a Joule-Thompson valve 24. The helium gas, as it is delivered through the heat exchangers 10 through 14, flows in a heat delivery relationship with the refrigeration stages 18 and 20, as well as in a heat delivery relationship with the low-pressure gas returning from the valve 24 through a continuous, low-pressure pressure conduit 26.

interposed between the conduit 26 and the Joule-Thompson valve 24 there is a heat load support 28 normally maintained at 42 K by a cooling coil 30. If desired, the load support 28 can be pre-cooled through a thermal switch, not

shown, but also associated with the refrigerator 16, for thus assuring the feasibility of maintaining the desired 4.2 K temperature at the load support 28.

The heat exchangers 10, I2 and 14, in conjunction with the stages 18 and 20 of the refrigerator 16, thus serve to pre-cool the helium gas prior to its being delivered and finally cooled at the J oule-Thompson valve 24 located at the final cooling stage 23. Once a temperature of 42 K is reached, the helium is liquified and delivered to the coil 30. However, after being subjected to a heat load at the support 28, the helium is returned to its vapor state and permitted to progress along the conduit 26 and returned to the compressor through the series of heat exchangers 10, 12 and 14. Since the gas progressing from the heat load support 28 is relatively cool, a heat exchange occurs at each of the heat exchangers as the gas is delivered through the system in a countercurrent flow.

In operation, the temperatures prevailing within the heat exchanger normally are sufficient to freeze and thus entrap contaminants, such as oil and water vapors normally found in the compressed helium. As a practical matter, it has been found that a substantial quantity of contaminants are frozen within the first heat exchanger 10 and therefore are captured and do not progress further into the system. Hence, it is possible to decontaminate the first heat exchanger 10 and thus substantially decontaminate the entire refrigeration system.

As best illustrated in FIG. 2, the heat exchanger 10 includes a first and a second cylindrical body, 32 and 34, respectively, between which there is arranged a concentric pair of helical chambers including an inlet chamber 36, normally maintained under high pressures, and a low-pressure chamber 38. The chamber 36 receives helium, as a gas, from the high-pressure side of the compressor while the low-pressure chamber 38 serves as a discharge chamber through which helium, as a gas, is returned from the load support 28, as the gas is circulated through the system. In practice, the inlet chamber 36 is provided with a pair of plug-like baffles 40 at its opposite ends through which the gas is permitted to ingress and egress. By utilizing chambers of a helical configuration, the effective length of the path followed by the flow of gas being delivered therethrough is maximized.

The conduit 15, at the inlet side of the chamber 36, is provided with an inlet segment of the conduit, designated 42, through which the gas is delivered from the compressor, while the conduit 15, at the outlet side of the chamber 36, is provided an outlet segment of the conduit, designated 44, through which the gas is delivered from the heat exchanger 10. The conduit 26 includes an inlet segment, designated 45, which serves as an inlet for the chamber 38 and an outlet conduit segment 46 for delivering gas from the chamber 38.

It is important to note that the outlet segment of conduit 44 terminates in a T fitting 47. This fitting connects the segment 44 of the conduit with a blow-down conduit 48 terminating at a discharge vent 50.

The vent 50 is in direct communication with the inlet chamber 36, through the blow-down conduit 48, so that fluids discharged from the chamber 36 into the outlet conduit 48 can be dumped into the atmosphere rather than being delivered to the next-in-line heat exchanger. However, within the conduit 48, between the chamber 36 and the vent 50, there is an on-off valve 52 which, when opened, accommodates passage of fluids to the vent 50. Of course, when the valve 52 is in its off" position, the vent 50 is isolated from the chamber 36 whereby venting of the chamber 36 is precluded and the helium flow is confined to the conduit 15.

At the outlet side of the chamber 38 and supported within the conduit segment 46, there is another on-off valve 54. This valve, when opened, permits a pneumatic circuit to be completed from the first heat exchanger 10 to the low-pressure side of the aforementioned compressor. However, once this valve is closed to an off condition, flow of fluids through the chamber 38 is interrupted and a stagnate condition is introduced within the chamber 38 for all of the heat exchangers, particularly the heat exchanger 10.

Therefore, it is to be understood that the T" fitting 47, the blow-down conduit 48, the vent 50 and the valves 52 and 54 together establish a decontamination system whereby frozen contaminants can be thawed within the heat exchanger 10 and expelled into atmosphere through the vent 50. By thus thawing and expelling the frozen contaminants, into the atmosphere, from the first heat exchanger 10, the refrigeration system substantially is decontaminated. Of course, the filter 22, interposed between the Joule-Thompson valve 24 and the heat exchanger 14, serves to trap contaminants which are not frozen in the various heat exchangers. However, and as a practical matter, it is possible to provide for system decontamination by simply employing the improved heat exchanger 10.

OPERATION It is believed that in view of the foregoing description, the operation of the device will be readily understood and it will be briefly reviewed at this point.

When operating, gas circulating under pressure is delivered from the high-pressure side of the compressor, not shown, through the conduit 15, the heat exchangers 10, 12 and 14, the cooling stages 18, 20 and 23, the filter 22, the Joule- Thompson valve 24, the coils 30 and the low-pressure conduit 26. After a determinable period, quantities of contaminants condense and freeze within the heat exchanger 10 thus requiring that decontamination operation be initiated.

Since the blow-down conduit 48 is coupled with the outlet conduit 44 through the T fitting 47, the temperature of the heat exchanger 10 can be elevated simply by opening the valve 52 and closing the valve 54, while continuing to deliver gas under pressure to the inlet chamber 36. This results in gas being delivered, at ambient temperatures, from the high-pressure side of the compressor through the inlet conduit segment 24, the chamber 36, the valve 52 and the vent 50.

Since the flow of gas through the conduit 26 is interrupted at the valve 54, the temperature of the heat exchanger 10 rapidly increases. As the temperature increases, frozen contaminants entrapped within the heat exchanger 10 are thawed and then discharged as a fluid from the chamber 36, through the blow-down conduit 48 and the valve 52, and ultimately dumped into the atmosphere through the vent 50. Once decontamination is achieved, the valve 52 is reclosed and the valve 54 reopened so that the system is permitted to function in a cooling mode wherein the helium again is circulated through the system.

Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is not to be limited to the illustrative details disclosed.

What is claimed is:

1. In a counterflow refrigeration system of the type including a plurality of series-connected heat exchangers, each having arranged therewithin a pair of concentric chambers defining a pair of countercurrent passages extending therethrough, the improvement comprising:

A. an inlet and an outlet conduit extending from each of said chambers for simultaneously conducting through said chambers oppositely flowing streams of gas; and

B. flushing means operatively associated with one chamber of said pair of chambers for flushing contaminants therefrom.

2. The improvement of claim 1 wherein the inlet conduit extending from said one chamber of said pair of chambers serves to deliver gas at ambient temperatures to the chamber while the outlet conduit extending from the other chamber of said pair of chambers serves to deliver gas from said other chamber, and said flushing means includes:

A. a blow-down conduit coupled with the outlet conduit of said one chamber;

B. an atmospheric vent communicating with said one chamber through said blow-down conduit;

C. a first on-off valve operatively coupled within the blowdown conduit for controlling the delivery of gas between said one chamber and said atmospheric vent; and

D. A second on-off valve associated with the outlet conduit extending from said other chamber for interrupting the 5 delivery of gas flowing from said other chamber, whereby when said first valve is opened and said second valve is closed gas delivered at ambient temperature through the inlet conduit extending from said one chamber is discharged to atmosphere through said vent while gas flowing from the inlet conduit extending from said other chamber through said heat exchanger is interrupted at said second valve.

3. In a method of decontaminating a refrigeration apparatus 

1. In a counterflow refrigeration system of the type including a plurality of series-connected heat exchangers, each having arranged therewithin a pair of concentric chambers defining a pair of countercurrent passages extending therethrough, the improvement comprising: A. an inlet and an outlet conduit extending from each of said chambers for simultaneously conducting through said chambers oppositely flowing streams of gas; and B. flushing means operatively associated with one chamber of said pair of chambers for flushing contaminants therefrom.
 2. The improvement of claim 1 wherein the inlet conduit extending from said one chamber of said pair of chambers serves to deliver gas at ambient temperatures to the chamber while the outlet conduit extending from the other chamber of said pair of chambers serves to deliver gas from said other chamber, and said flushing means includes: A. a blow-down conduit coupled with the outlet conduit of said one chamber; B. an atmospheric vent communicating with said one chamber through said blow-down conduit; C. a first on-off valve operatively coupled within the blow-down conduit for controlling the delivery of gas between said one chamber and said atmospheric vent; and D. a second on-off valve associated with the outlet conduit extending from said other chamber for interrupting the delivery of gas flowing from said other chamber, whereby when said first valve is opened and said second valve is closed gas delivered at ambient temperature through the inlet conduit extending from said one chamber is discharged to atmosphere through said vent while gas flowing from the inlet conduit extending from said other chamber through said heat exchanger is interrupted at said second valve.
 3. In a method of decontaminating a refrigeration apparatus of a type including a plurality of series-connected heat exchangers each including a pair of concentrically oriented countercurrent passages for cooling gases to cryogenic temperatures, the step of, interrupting the flow of gas through one of the chambers of a first-in-line one of said heat exchangers, and delivering gas at ambient temperatures through the other chamber of the heat exchanger and venting the delivered gas to atmosphere as it is discharged from said other chamber, whereby the temperature of said one heat exchanger is elevated for melting and dispelling frozen contaminants disposed therewithin. 